PREDICTION OF A PROCESS WINDOW FOR THE INVESTMENT-CASTING OF DENDRITIC SINGLE-CRYSTALS

Large dendritic single crystal blades operating in jet engines or land -based turbines are commonly produced in industrial plants. However, t he production cost of some of these parts remains high due to the seve ral types of defect which may appear during the different stages of th e investment casting process. The prevention of stray crystal formatio n during solidification is the main problem which has to be faced by e ngineers. Analytical developments are first presented in order to defi ne conditions under which single crystal growth is favored. This proce ss window is described in a space where the thermal gradient and the w ithdrawal speed of a Bridgman furnace apparatus are the controlling pa rameters. The limits of this process window are then refined in order to determine the influence of other parameters such as the crystallogr aphic orientation of the single dendritic grain, the size of the platf orm in which the single grain has to extend, the growth kinetics of th e dendrite tips, or the existence of a lateral thermal gradient. (C) 1 997 Elsevier Science S.A.